The present invention relates to a calibration apparatus, an adaptive array apparatus, a calibration method, a program recording medium for recording a computer-readable program, and a program, all of which are for measuring the differences of the transfer characteristics between a transmission unit and a reception unit of a plurality of radio systems within an adaptive array apparatus designed for radio communication.
With the recent increase in mobile stations such as PHS devices and mobile phones, there is an increasing social need for more effective use of radio wave frequency resources. An example of a communication method that addresses this need is the spatial multiplexing method.
The spatial multiplexing method is a communication method that involves the usage of an adaptive array apparatus that forms a different directivity pattern (called an adaptive array pattern) for each of a plurality of mobile stations. By doing this, the adaptive array apparatus is able to perform communication functions by multiplexing the transmission and reception signals of the plurality of mobile stations simultaneously on the same frequency.
An adaptive array apparatus includes a plurality of radio units made up of an antenna, a transmission unit, and a reception unit. And this apparatus forms directivity patterns (called array antenna patterns) for the entire antenna by adjusting the amplitudes and phases of the transmission signals and reception signals inputted to and outputted from each radio unit. More specifically, the array antenna patterns are formed by weighting the amplitudes and phases of the transmission signals and reception signals inputted to and outputted from each radio unit using a weight coefficient (also called a weight vector). The calculation of weight vectors is performed by a DSP (Digital Signal Processor) within the adaptive array apparatus.
When an adaptive array is used in a mobile phone system, the mobile phone unit has physical limitations such as size and possible number of antennas, making it impossible for the mobile phone to perform the function of controlling the directivity pattern. Therefore, it is the radio base station that forms the directivity patterns both at times of reception and times of transmission. In that case, the array antenna pattern formed by the radio base station at the time of transmission is same as the one that has been optimally formed at the time of reception.
However, even if the weight vector calculated at the time of reception is used at the time of transmission, it is not always the case that the same array antenna pattern will be formed for transmission and reception. This is due to the fact that, within each radio unit, the transfer characteristics of the transmission unit vary from those of the reception unit. These differences stem, for example, from the fact that the units are two physically separate circuits and there are variations between the characteristics of the circuit elements. In particular, this variation between the characteristics of the circuit elements come about in LNAs (Low Noise Amps) found in reception units and HPAs (High Power Amps) found in transmission units, these amps varying individually or undergoing temperature changes in certain usage environments. Due to these factors, variation comes about in the transfer characteristics such as phase rotation amounts and amplitude fluctuation amounts produced when a signal is passed through the transmission unit and the reception unit.
The differences between the transfer characteristics of reception units and transmission units have direct influences to errors in array antenna patterns at times of receiving and transmitting. For this reason, it is necessary that differences in transfer characteristics between transmission units and reception units be measured in order to perform calibration to compensate for those differences An example of such a calibration method can be found in Japanese Laid-Open Patent Application No. H11-312917, titled Array Antenna Apparatus
This array antenna includes, as additional equipment, a calibration-specific desired signal generation means, a calibration-specific interference signal generation means, an electrical power control means for controlling the electrical power of the calibration-specific interference signal generation means, a combining means for combining the calibration-specific desired signal with the calibration-specific interference signal whose electrical power is controlled, and a distribution means for distributing the combined signal to the various antennas, so as to compensate for the transfer characteristics within a reception system.
This additional equipment is required within the adaptive array apparatus of the prior art to assess the difference between transfer characteristics of transmission circuits and reception circuits in each separate radio unit, causing a problem wherein the scale of the circuits are increased. In other words, the problem with the prior art is that the scales of its circuits are increased in order to include a calibration-specific circuit that would not be required in regular communication.
In light of the above problems, an object of the present invention is to provide a calibration apparatus, an adaptive array apparatus, a calibration method, a program recording medium and a program all of which are able to perform calibration processes without having additional equipment in the apparatus whose transfer characteristics are to be measured.
In order to achieve the above object, the present invention provides a calibration apparatus that measures a correction value for a radio terminal which, for a purpose of performing radio communication by forming an array antenna pattern, includes at least a first radio unit and a second radio unit, each made up of a transmission unit, a reception unit, and an antenna, the calibration apparatus comprising: a first antenna; a second antenna; a control means for controlling the first radio unit and the second radio unit to perform transmission of signals with an array antenna pattern being formed, using a weight vector by which a directivity is oriented toward the first antenna and a null is directed toward the second antenna; and a measuring means for measuring transfer characteristics that are relative between the first radio unit and the second radio unit on the basis of a signal level of the signals received by either the first antenna or the second antenna.
With this arrangement, it is possible to measure the relative transfer characteristics that are relative between the first radio unit and the second radio unit, on the basis of the level of the signals received by the first antenna and the second antenna, by controlling the first radio unit and the second radio unit, which are originally located in the radio terminal, to perform transmission of signals with an array antenna pattern being formed; therefore, there is an effective result that calibration can be performed without having additional calibrating equipment in the radio terminal whose transfer characteristics are to be measured.
The calibration apparatus may have an arrangement wherein the control means controls the second radio unit to fluctuate, during the transmission by the first radio unit and the second radio unit, a phase and an amplitude of the signal transmitted, and the measuring means measures a phase fluctuation amount and an amplitude fluctuation amount as the transfer characteristics on the basis of the phase and the amplitude at such a time when the signal level of the signals received by the second antenna is minimum during the fluctuation.
With this arrangement, the phase fluctuation amount and the amplitude fluctuation amount can be measured by fluctuating the phase and the amplitude of only the signals transmitted by the second radio unit during the transmission performed by the first radio unit and the second radio unit, and matching the null direction with the direction of the second antenna.
The calibration apparatus may further comprise a transmission means for transmitting, on a same frequency, a desired signal from the first antenna, and an interference signal from the second antenna, wherein the control means (i) controls the radio terminal to calculate a weight vector by which the interference signal can be eliminated and the desired signal can be received by the first radio unit and the second radio unit, and then (ii) controls the first radio unit and the second radio unit to perform the transmission of the signals using the weight vector calculated.
With this arrangement, it is possible to match accurately the null direction in the array antenna pattern at the time of reception and the null direction in the array antenna pattern at the time of transmission.
The present invention further provides an adaptive array apparatus including a plurality of radio units, each made up of a transmission unit, a reception unit, and an antenna, the adaptive array apparatus comprising:
a selecting means for selecting a radio unit among the plurality of radio units; and
a control means for controlling the selected radio unit and one of unselected radio units to perform transmission of signals between each other in order to measure transfer characteristics of the selected radio unit on the basis of the signals received.
With this arrangement, the control means controls the selected radio unit and one of unselected radio units to perform transmission of signals between each other in order to measure transfer characteristics of the selected radio unit on the basis of the signals received; therefore, there is an effective result that the transfer characteristics can be measured without having an additional circuit. Furthermore, if only one radio unit is selected, the transfer characteristics of the particular radio unit can be measured, whereas, if two radio units are selected, the transfer characteristics that are relative between those two radio units (that is to say, the relative transfer characteristics) can be measured.
The adaptive array apparatus may have an arrangement wherein the selecting means selects another radio unit after the measuring by the control means, and the control means calculates a correction value for each of the radio units on the basis of the transfer characteristics measured for each of the radio units.
With this arrangement, there is an effective result that, in addition to the effect already mentioned, it is possible to measure the transfer characteristics of each radio unit, and calculate the corrections value for each radio unit from the result of measuring, since the selecting means selects each of all the radio units in turn.
The adaptive array apparatus may have an arrangement wherein the selecting means selects two radio units, the two selected radio units perform the transmission of the signals with such an array antenna pattern being formed in which a null is directed toward the antenna of one of the unselected radio units, while the two selected radio units fluctuate one or both of a phase and an amplitude at one of the two selected radio units, and the control means determines that the transfer characteristics are one or both of the phase and the amplitude at such a time when a signal level of the signals received by the radio unit toward which a null is directed is minimum during the fluctuation.
With this arrangement, there is an effective result that, in addition to the effects already mentioned, it is possible to easily measure the deviation in the array antenna patterns at the time of transmission by (i) having the selected radio units form such an array antenna pattern in which a null is directed toward the antenna of another radio unit, so as to match the null direction at the time of reception with the null direction at the time of transmission (in other words, that is when the level of the signals received is the minimum), and (ii) measuring one or both of the phase and the amplitude.
The adaptive array apparatus may have an arrangement wherein the two selected radio units form the array antenna pattern in which a null is directed toward the antenna of the unselected radio unit, by using a weight vector obtained at such a time when the two selected radio units perform an array-reception while eliminating the signal transmitted by one of the unselected radio units.
With this arrangement, there is an effective result that, in addition to the effects already mentioned, it is possible to easily form an array antenna pattern in which a null is directed by using the same weight vector at the time of array-reception for the array-transmission as well.
The present invention further provides an adaptive array apparatus including a plurality of radio units each made up of a transmission unit, a reception unit, and an antenna, the adaptive array apparatus comprising: a selecting means for selecting four radio units among the plurality of radio units as a first radio unit, a second radio unit, a third radio unit, and a fourth radio unit; and a control means for (a) controlling the third and the fourth radio units to perform an array-transmission using a weight vector by which a directivity is oriented toward the antenna of the first radio unit and a null is directed toward the antenna of the second radio unit; and (b) measuring transfer characteristics that are relative between the third radio unit and the fourth radio unit on the basis of a signal level of the signals received by either the first radio unit or the second radio unit.
With this arrangement, there is an effective result that, without having an additional circuit, it is possible to measure the relative transfer characteristics based on the level of the signals received by controlling the third radio unit and the fourth radio unit that are selected to perform an array-transmission.
The adaptive array apparatus may have an arrangement wherein the selecting means repeats selecting four radio units among the plurality of radio units, until each of all the plurality of radio units gets selected once as a fourth radio unit, and the control means calculates a correction value for each of the plurality of radio units using one of the plurality of radio units as a standard of relativity, on the basis of the transfer characteristics measured for each of the radio units.
With this arrangement, there is an effect result that, in addition to the effects already mentioned, it is possible to calculate a relative correction values for each of the radio units using one of the radio units as a standard of relativity.
The adaptive array apparatus may have an arrangement wherein the control means further judges whether the transfer characteristics are correct by checking if either a sum or a product of the transfer characteristics of each of the radio units that are relative fits in a predetermined range.
With this arrangement, it is possible to easily judge whether the measured transfer characteristics are correct by using the relativity of transfer characteristics of each radio unit; consequently, it is possible to avoid using incorrect correction values.
The present invention further provides a calibration method used in an adaptive array apparatus including a plurality of radio units, each made up of a transmission unit, a reception unit, and an antenna, the calibration method comprising: a selecting step of selecting a radio unit among the plurality of radio units; and a measuring step of controlling the selected radio unit and one of unselected radio units to perform transmission of signals between each other in order to measure transfer characteristics of the selected radio unit on the basis of the signals received.
With this arrangement, it is possible to measure the transfer characteristics of the radio units without having additional equipment.
The present invention further provides a program recording medium storing a computer-readable program to be executed by a computer in an adaptive array apparatus including a plurality of radio units, each made up of a transmission unit, a reception unit, and an antenna, the program instructing the computer to execute: a selecting step of selecting at least one radio unit among the plurality of radio units; and a measuring step of controlling the selected radio unit and one of unselected radio units to perform transmission of signals between each other in order to measure transfer characteristics of the selected radio unit on the basis of the signals received.
The computer in the adaptive array apparatus that reads the program is able to measure the transfer characteristics of the radio units without having additional equipment.